High frequency circuit



Feb. 26, 192.5.v

HIGH FREQUENCY C IRCUIT Filed March 1, 1933 Invent OYZ Stewart Becker IM/A466 s. .VBECKER 1,992,805

Patented Feb. 26, 1935 PATENT OFFICE HIGH FREQUENCY CIRCUIT StewartBecker, Schenectady, N. Y., assignor to General Electric Company, acorporation of New York Application Marchl, 1933, Serial No. 659,084

9 Claims.

My invention relates to high and ultra-high frequency receivers, andmore particularly to a tuning unit and circuit for a multi-rangereceiver.

In radio receivers for high and ultra-high frequencies it has beencustomary to provide plug-in inductors sothat the various frequencyranges may becovered efficiently, but such an arrangement isinconvenient and uneconomical. Tapped inductors generally have beenavoided because the unused portions thereof reduce the efiiciency of theinductors to such a degree as to be undesirable. In accordance with myinvention, a single inductor is employed for a plurality of highfrequency ranges without materially sacrificing efiiciency. This isaccomplished by maintaining in'the tuning circuit a high inductance tocapacitance or L/C ratio, by connectinga portion of the tuning inductorin a manner to form one of a plurality of circuits having a low L/Cratio, thereby reducing the effective inductance in the tuning circuitsufiiciently to alter the tuning range thereof. 3

An object of my invention is to provide an improved multi-range tuningelement which will be simple, efficient and economical.

A further object of my invention is to provide a tuning circuit having ahigh L/C ratio and means for reducing the inductance therein byconnecting in succession the unused portion of a tuning inductorin amanner to form a plurality of circuits having a low L/C ratio whereby aplurality of tuning ranges are obtained.

A still further object of my invention is to provide a tuning unit for aregenerative receiver whereinthe effectiveness of the regeneration orreaction inductor is adjusted simultaneously with the adjustment of thetuning inductor for the different frequency ranges, wherein the unusedportion of the tuning inductor is connected to form a low L/C ratiocircuit, as compared to the tuning circuit having a high L/C ratio.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, both as to its organization and method of operation,together with further objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwiththe accompanying drawing in which the figure shows a radio receiverembodying my invention. V

Referring to the figure in the drawing, I have illustrated therein aradio receiver having input terminals 1 which may be connected to an antenna and ground or any other source of high frequency signals. Theseterminals are connected to the grid and cathode of an electron dischargedevice 2. A source of biasing potential 3 and a coupling resistor 4 areconnected between the cathode and the grid of the discharge device. Thedischarge device may be of the three or fourelement type. If afour-element type is used, as is shown in the figure, the screen grid issupplied with a suitable source of potential connected betweenthescreengrid lead and the ground. The 10 anode circuit of the discharge device 2is connected through an inductor 5 to the positive terminal of a sourceof potential which has its negative terminal connected to ground. Avariable capacitor 6 is arranged to be efiective across the 15 entireinductor 5. The circuit comprising the inductor 5 and the variablecapacitor 6 constitutes an arrangement having a high inductance tocapacitanc'eor L/C ratio. The lower extremity of the inductor 5 isprovided with a plurality of taps 20 which may be connectedto a fixedcapacitor 7, which in turn is connected -to ground. The circuitcomprising a portion of the inductor 5 and the capacitor"! has a lowinductance to capacitance or L/C ratio. The upper extremity of thetuning circuit comprising the inductor 5 and the capacitor 6 is coupledby a coupling or grid capacitor 8 to the control grid of a secondelectron discharge device 9. A grid leak resistor 10 connected betweenthe control grid and the cathode of the discharge device completes thegrid circuit thereof. If the discharge device 9 is of the fourelementtype a screen grid may be connected to a potentiometer 11 which isbridged across a suitable potential and adjustment of this potentiometerwill operate as a regeneration control device. The anode of the electrondischarge device 9 is connected to a regeneration or reaction inductor12 which is'arranged in fixed relation to the tuning inductor 5. A radiofrequency choke 13 connected in series with the'reaction inductor 12serves to prevent the radio frequency currents from being impressed uponthe output coupling circuit which comprises an inductor 14 andcapacitors 15 and 16. The anode of the discharge device is supplied withpotential from a source connected between ground and one extremity ofthe inductor 14. A plurality of fixed capacitors '17, 1a, 19 and 20having different capacity values 7 are arranged with a common connectionto ground. It is to be understood that the capacitors 17, 18, 19 and. 20may be of the adjustable type which when adjusted are fixed compared tothe usual variable capacitor. A conductor 21 which is connected to thehigh potential side of the reaction inductor 12 is connected to a switch22 whereby any one of the capacitors 17 to 20 may be connected betweenthe reaction coil and ground to vary the regenerative effect thereof.The switch 22 is mechanically linked for simultaneous operation with aswitch 23 which serves as a means for selectively connecting thecapacitor 7 to. the various taps of the tuning inductor 5.

A receiver :as described embodies a coupling stage 2, which, whilepreferable, is not essential and does not constitute a part ofapplicantsinvention. This coupling stage, comprising a discharge device2 and associated elements, isian aperiodic circuit having no frequencycharacteristic. In order to tune the detector circuit '9 through any oneof a plurality of high frequency ranges the proper range is selected bythe switches 22 and 23 which simultaneously provide the proper reactioneffect of the inductorl2 andthe corresponding frequency range of theinductor 5 and the tuning element fi. As the switch 23 is rotatedcounter-clockwise circuits having different values :of inductance andcapacitance. are coupled to the normal tuning circuit-comprisingtheinductor 5iandthe capacitor 6. The capacitor 7 however has a.capacity valuev relativelylarge compared to the variablecapacitor.6,:and thus the circuit comprising a portion of the inductor 5and the capacitor 7 has a relativelyalow L/ C ratio. The effect ofcoupling alowL/Cratiocircuit to a tuning circuit having ahighL/Cratio inthis arrangement is such I that while reducing @the effective inductanceof the tuning circuitno material losses are introduced-such aswouldbe-encountered if the tap portionof the tuning inductor 5 were merelyshortcircuitsor leftunused. Such unused :portions ordinarily .havethedetrimental effect (if-permitting parasitic circulating currents tobeset upin the unused inductorportion thereby reducingthe eificiencyzof,the useful circuit by .suchan amount as to'seriously reducethesensitivity' of the receiver.

It will "be apparent thatan arrangement comprising theinductor 5 andthe-capacitors-6 and '7 of themselves without the reaction inductor 12may be utilizedas coupling membcrsiina cascade radiofrequency amplifier*as welLas in the circuit shownin the drawing. Applicants arrangementhas the advantage that a single inductor and. a

simple switching mechanism provides a compact economical .tuningelement-suitable for operation at high and ultra-high frequencies suchasare received on the multi-range.receivers.

While I have shown and described my invention in connection withcertainspecificembodiments. it will, of course, be understood that I donotwis-h to be limited thereto-,Jsince it is apparent that" theprinciples herein- .disclosedzare susceptible of numerous otherapplications, and modifications may be made in the'circuit arrangementsand in the instrumental-ities employed without departing from thespirit. and. scope. of: my invenrelativelylarge capacitor to one of a.plurality of intermediate points on said inductor to reduce the;efiectiveinductance thereof wherebyythe frequency range of said circuitis changed.

2..I-n, multi-range radio apparatus, the combination of a tapped tuninginductor arranged in parallel with a variable capacitor, said circuithaving a high L/C ratio, wherein L is inductance and C is capacitance, afixed capacitor connected to one extremity of said inductor, and meansfor connecting selectively'said fixed capacitor to the taps of saidinductor, said fixed capacitor and the portion of saidinductorinshunttherewith constituting a circuit having a low L/C ratio, whereby saidcircuits cooperate efficiently to change the normal frequency range ofthe circuit comprisin'g said inductor and variable capacitor.

,3. In a multi-range regenerative radio receiver,

the combination of a tapped grid circuit inductor having a variabletuning capacitor connected across saidinductor, a fixed capacitorconnected to one extremity of said inductor, a regeneration inductorcoupled in fixed relation to said first inductor, means for selectivelycontrolling the effect of said regeneration inductor, and a common means.forcontrolling said last mentioned means and :for selectivelyconnecting said-fixed capacitor to said .tapson said gridcircuitinductor whereby different frequency ranges are obtained for saidgrid icircuit inductor together with a correspondingregenerative efiect.

4. In a regenerative radioureceiver, the combination of a tapped gridcircuit inductor, a .reaction inductor, a plurality of fixed capacitorshaving a common connection, a uni-control means forconnectingselectively said reaction inductor to different fixed. capacitors andfor connectingione .ofsaidfixed capacitors to a corresponding oneof saidtaps on said grid circuit inductor whereby different frequency rangesareobtained, and. a variable capacitor connected in shunt .to saidgridcircuit inductor fortuning said circuit through each. frequency range,said variable capacitor and saidgrid circuit inductor being connected tothe common connection of said fixed capacitors.

5. In a radio apparatus, a tuned circuit comprising aninductor and. avariable capacitor and having ahigh inductance to capacitance ratio, areaction inductor arranged in fixed relation to said first inductor, aplurality of different fixed and said reaction inductor are adjusted foroperation over-av plurality of frequency ranges.

-.6.. :In' a multi-range regenerative radicreceiyer, the combinationof agrid. circuit inductor having a variable tuning. capacitor connectedacross said inductor, a large capacitor connected to one extremity ofsaid inductor, a regeneration inductor coupled to said firstinductor,means for selectively controlling the effect of saidregenerationinductor, and a common means for controlling said last-mentioned meansand for selectively connecting said second capacitor to. differentpoints on said inductor whereby different frequency ranges are obtainedfor said grid circuit inductor together with a different regenerativeeffect.

7. In multi-range radio apparatus, the combination of a circuit having ahigh inductance to capacitance ration and comprising a tapped inductorand a variable capacitor, a second capacitor connected to one extremityof said inductor, and means for connecting selectively said capacitor tothe taps of said inductor, said second capacitor and the portion of saidinductor in shunt therewith constituting a circuit having a lowinductance to capacitance ratio, whereby said circuits cooperateefiiciently to change the normal frequency range of the circuitcomprising said inductor and variable capacitor.

8. In combination, a tuned circuit comprising an inductance andcapacitance, said circuit having a large ratio of inductance tocapacitance, a large capacitance, and means to connect said largecapacitance across a variable portion of said inductance, saidcapacitance being sufiiciently large to produce with the portion ofinductance across which it is connected a circuit having smallinductance to capacitance ratio.

9. In combination, an inductor, a variable capacitor and a fixedcapacitor, means to connect said fixed capacitor across a variableportion of said inductor, thereby to adjust said inductance foroperation in different frequency ranges, said capacitor having suchlarge capacitance that the circuit formed by said capacitor and theportion of the inductor across which it is connected has a low ratio ofinductance to capacitance, and means including said variable capacitanceto form with said inductance a circuit having high inductance tocapacitance ratio, said circuit being tuned to the operating frequency.

STEWART BECKER.

